The invention relates to a system for determining boil states of the contents of cooking utensils while being heated, and to a method for determining boil states. More specifically, the invention relates to an acoustic sensor system for use in determining boil states, and an associated method for determining boil states using an acoustic sensor system.
Boiling water or other fluids or foods (generically "liquids") is a common step in cooking; for instance it is one of the most common uses for a range. It is typically desirable to closely monitor the boil phase of the liquid during such processes, i.e., to identify the pre-simmer, simmer onset, simmer and/or boil phases. In this regard, the pre-simmer phase is generally characterized by a calm liquid and the simmer onset phase is the initial, slow bubbling of the liquid characterized by the appearance of individual bubbles. During the simmer phase, bubbles appear in jets creating the effect commonly referred to as simmering. Finally, in the boil phase, the bubbling of the liquid is generalized, resulting in the familiar turbulence of a boiling liquid. These phases can be identified by experts and experienced cooks. The formation and collapse of the bubbles during the phases create an acoustic signature which changes with the size and number of the bubbles, the rate of their formation, their collapse, and the temperature gradient in the liquid. This acoustic response includes the audible component, which can be easily observed when cooking, as well as responses in various frequency bands. It is also affected by factors including the type of cooking vessel and any ingredients in the liquid.
The boil phase is monitored for a number of reasons. First, many cooking processes require that the liquid be attended to upon identification of a particular boil phase, e.g., reducing the heat after the liquid reaches a boil. In addition, the boil phase may be monitored to reduce heat upon boiling so as to prevent boil-over which can result in a burned-on mess or, in the case of gas ranges, extermination of the cooking flame. In addition, the boil phase may be monitored to reduce heat after the liquid reaches a boil, either to reduce it to a simmer for cooking purposes or to prevent boil-over. Boil-over can result in a burned on mess or, in the case of gas ranges, extermination of the cooking flame. Moreover, a liquid not monitored when boiling can boil dry, resulting in burning of the food, damaging the cooking utensil, as well as presenting potential fire hazards.
Generally, the boil phase is monitored visually. Such visual monitoring can interfere with the user's ability to prepare other foods or be otherwise disposed during heating of the liquid. Moreover, a busy or inexperienced cook may fail to accurately, or in a timely manner, identify a boil phase of interest.
Increasingly, manufacturers seek to provide, and consumers desire to have, appliances with a greater degree of automated operation and control. With the increasing affordability of integrating computing power into an appliance, there exists a potential to provide the increased levels of automated control. However, information gathering tools or devices that interact with a computer or microcontroller in monitoring or controlling the operation of the appliance must also have desirable cost and performance attributes.
For cooking appliances generally, and for electric and gas range cooktops specifically, automation or partial automation of control of the cooking process, or monitoring of cooking on a cooktop, has traditionally focused on temperature monitoring or sensing. Various temperature sensors have been proposed for sensing the temperature of a surface heating unit or a cooking utensil positioned thereon or food contents therein, and for controlling the heat input to the heating unit, based upon the sensed temperature. Such sensors have commonly been proposed for use in connection with glass-ceramic radiant cooktops, and purport to enable detection and control of cooking states. The sensors essentially measure temperatures directly, and are frequently coupled to the heating unit control system to provide feedback to the control system.
Temperature-based sensing systems for range cooktops may indirectly or inferentially provide information regarding a boil state of a liquid contained in a utensil and being heated on the cooktop. However it continues to be a problem in cook-top sensing and control to provide a method for reliably determining the boil state since the correlation between temperature and boil state depends on a number of variables including, but not limited to, type of liquid, the amount of liquid, any additives, the position of the utensil, and the utensil's warpage. For instance, it is well known that the addition of salt into water raises the boiling temperature. Environmental conditions such as elevation can also affect the temperature associated with boil states. Finally, the position of the temperature sensor and its calibration can also have a significant impact on achievable accuracy. The general need then is to develop an approach to boil state determination that is more robust to cooking modalities, vessels used, various user interactions, and other variations, or disturbances, in the equipment or environment.